The present invention is directed to emitter electrodes for gas ionizers and, more specifically, to a gas ionizer emitter electrode formed of or coated with a carbide material such as silicon carbide.
Ion generators are related generally to the field of devices that neutralize static charges in workspaces to minimize the potential for electrostatic discharge. Static elimination is an important activity in the production of technologies such as large scale integrated circuits, magnetoresistive recording heads, and the like. The generation of particulate matter by corona-producing electrodes in static eliminators competes with the equally important need to establish environments that are free from particles and impurities. Metallic impurities can cause fatal damage to such technologies, so it is desirable to suppress those contaminants to the lowest possible level.
It is known in the art that when metallic ion emitters are subjected to corona discharges in room air, they show signs of deterioration and/or oxidation within a few hours and the generation of fine particles. This problem is prevalent with needle electrodes formed of copper, stainless steel, aluminum, and titanium. Corrosion is found in areas under the discharge or subjected to the active gaseous species NOx. NO3 ions are found on all the above materials, whether the emitters had positive or negative polarity. Also, ozone-related corrosion is dependent on relative humidity and on the condensation nuclei density. Purging the emitter electrodes with dry air can reduce NH4 NO3 as either an airborne contaminant or deposit on the emitters.
Surface reactions lead to the formation of compounds that change the mechanical structure of the emitters. At the same time, those reactions lead to the generation of particles from the electrodes or contribute to the formation of particles in the gas phase.
Silicon and silicon dioxide emitter electrodes experience significantly lower corrosion than metals in the presence of corona discharges. Silicon is known to undergo thermal oxidation, plasma oxidation, oxidation by ion bombardment and implantation, and similar forms of nitridation. Some have tried to improve silicon emitters by using 99.99% pure silicon that contains a dopant such as phosphorus, boron, antimony and the like. For example, U.S. Pat. No. 5,650,203 (Gehlke) discloses silicon emitters containing a dopant material. However, even such high purity doped silicon emitters suffer from corrosion and degradation.
Another approach is to form emitter electrodes from nearly pure germanium or from germanium with a dopant material. For example, U.S. Pat. No. 6,215,248 (Noll), the contents of which are incorporated by reference herein, discloses germanium needles or emitter electrodes for use in low particle generating gas ionizers and static eliminators. While such germanium emitter electrodes have proven to be less susceptible to corrosion and degradation than metallic emitter electrodes and silicon emitter electrodes with a dopant, there is a need for an emitter electrode that produces or causes even less metallic and/or non-metallic contamination with enhanced resistance to erosion.